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Draw shapes
Draw same shapes of disk on a 5.5 mm thick plywood using previous template made of cardboard.Tentatively, quantity of required disks is equal to (Height of horn) / (Thickness of the disk). For Helix-L70, it is 42 (= 230/5.5). The thickness of the disks used is 5.5 mm each. Thickness of each glue layer may be 0.4 mm, and then total thickness of glue layer is about 16 mm. This is equivalent to 3 disks. Therefore quantity of required disks is 39 (= 42 - 3). | ||||||||||||||||||
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Drill and cut
Drill two holes on each disk and cut them using jigsaw as shown in the left picture. | ||||||||||||||||||
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Draw datum lines (black)
Extend an edge line, and draw a datum line on periphery of a disk as shown in the left picture.
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Draw displacement lines (red)
Total displacement is 690 mm. This is nearly equal to 90 x 3.14 x 2.5 = 707 mm where 90 is diameter of disk and 2.5 is rotation number of partition. At the lower part of horn, displacement/disk is smaller and inclination of partition is steeper. | ||||||||||||||||||
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Glue
Round off the edge of disks using a file, and glue them with shifting one by one a length of above-mentioned displacement/disk.Rub extra glue into around periphery. | ||||||||||||||||||
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Finished
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Q: I'd like to use the disk-method for building the spiral passage. How to calculate the specific displacement values for either Helix-h75 or Helix-h88? A: The spiral horn can be opened-up on a flat plane as the following figure. The peripheral length is 298 mm (= 95 mm x 3.14) based on an assumption that the outer diameter of the spiral is 95 mm (= inner diameter 75 mm + wall thickness 10 mm x 2). The spiral partition plate can be indicated by the lines drawn at successively steeper slants. A displacement depends on the thickness of the disks as shown in the figure and may be calculated easily. The box of Helix-h75 should be expanded for adapting to the thick wall. |
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Mr. Jim living in Athens (Greece) had built a glass spiral using Plexiglas instead of wood. Details are here. Spiral building Speaker building | |
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The disk method always remains long and laborious (tedius) but a little less than cut them individually.
I have used one hand router with a jig in order to cut a perfect hole. I built it home-made, but I know is also sold in the well supplied home depot (very popular between DIY hi-fi cabinet). Its easy and fast : make a hole in the center of the disc and insert the pivot of the jig, then cut them. You will be able to obtain a good precision in roundness in everyone of the three circular cuts of the disc: inside and outside of the outer tube and ouside of the inner tube. You will have to only be careful to stop the cut before the two straight line. Then the last shot: cut with jigsaw (the alternatives saw) the two straight lines from the internal diameter of outer tube to outer diameter of the inner tube. I have put, one over the other, 4 plywood sheets of okum…~ plywood (total height 16 milimeter, 4x4), therefore have obtained 4 disk from every cut (the Helix L100 I want to build demanded the use of 81 disk each speaker!). I have glue them with vinil glue and used two sturdy discs with 4 clamp in order to distribute the pressure uniformly. Please to note that I also have used a wood rod in the center of the disk which I have inserted one disc after the other. The rod allows to rotate the discs to allow to put them in correct position, but it prevents also they form moving while they come glue. Then I have used a hand power tool in order to get a smooter helix and to obtain a more homogenous surface with little discs steps. However, the use of a plywood of only 4 mm already allows to have a better surface than a discs of greater thickness. | |
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 The center is an Acoustical speaker and the right is ME2 designed by Lynn Olson. |
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Long and thin wood plates were used for constructing a pair of spiral for H75 as shown above by Mr. Iwanami. He had built a pair of single helix and a pair of double helix simultaneously with this method. He purchased several thin Japanese cypress plates (3x10x910 mm) sold at DIY shop, and cut it to 76 mm long plates. Then he bored a hole with 3 mm diameter to each plate. Bamboo rods with 3 mm diameter were used as the central axes. Plates applied an adhesive were piled on top of another plate along a paper guide through the central axis, which was fixed on a base plate. He felt a sturdier material than bamboo should be used as the central axes because it tended to twist. He found extreme difficulty for single helix for maintaining right angle between plates and a central axis. It was required to adjust the angle frequently. At the last, he applied putty on the helix completed, and then, rounded its outer circumference with a rasp. He said that sound characters were not different between single helix and double helix. | |
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